New Post: How is it possible with NO ORDERS

I receive the following - on occasion - with a new store setup - that works fine with Sandbox - and when I get this error I go to BO -> Orders to find NO ORDERS ON FILE?

System.OverflowException: Arithmetic operation resulted in an overflow.
at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value)
at NEvoWeb.Modules.NB_Store.Gateway.PayPalIPNParameters..ctor(NameValueCollection requestForm)
at NEvoWeb.Modules.NB_Store.Gateway.GatewayPayPal.AutoResponse(Int32 PortalID, HttpRequest Request)

Details: NB store 2.38 - which begs the question: Should I install V3?

My IIS Logs show the IPN post from PayPal as a 301 (permanent redirect) with the follow up as a 200 status?
I am lost!